Method for preparing ge1-x-ysnxey (e=p, as, sb) semiconductors and related si-ge-sn-e and si-ge-e analogs

ABSTRACT

A process for is provided for synthesizing a compound having the formula E(GeH 3 ) 3  wherein E is selected from the group consisting of arsenic (As), antimony (Sb) and phosphorus (P). GeH 3 Br and [CH 3 ) 3 Si] 3 E are combined under conditions whereby E(GeH 3 ) 3  is obtained. The E(GeH 3 ) 3  is purified by trap-to-trap fractionation. Yields from about 70% to about 76% can be obtained. The E(GeH 3 ) 3  can be used as a gaseous precursor for doping a region of a semiconductor material comprising Ge, SnGe, SiGe and SiGeSn in a chemical vapor deposition reaction chamber.

RELATED APPLICATION DATA

This application is based on and claims the benefit of U.S. ProvisionalPatent Application No. 60/478,480 filed on Jun. 13, 2003, the disclosureof which is incorporated herein by this reference.

STATEMENT OF GOVERNMENT FUNDING

The United States Government provided financial assistance for thisproject through the National Science Foundation under Grant No. DMR0221993 and through the Army Research Office Grant No. DAA 19-00-0-0471.Therefore, the United States Government may own certain rights to thisinvention.

BACKGROUND

This invention relates generally to semiconductor materials and, moreparticularly, to doping and superdoping in situ a broad family ofSi-based semiconductors such as Ge, SnGe, SiGe, and SiGeSn with As, P,and Sb (Group V element).

It has been known for many years—on theoretical grounds—that the SnOealloy system and the SiGeSn alloy system should have properties thatwould be very beneficial in microelectronic and optoelectronic devices.This has stimulated intense experimental efforts to grow such compounds.For many years the resulting material quality has been incompatible withdevice applications. Recently, however, we successfully synthesizeddevice-quality SnGe alloys directly on Si substrates. See M. Bauer, J.Taraci, J. Tolle A. V. G Chizmeshya, S. Zollner, J. Menendez, D. J.Smith and J. Kouvetakis, Appl. Phys. Lett 81, 2992 (2002); M. R. Bauer,J. Kouvetakis, D. J. Smith and J. Menendez, Solid State Commun. 127, 355(2003); M. R. Bauer, P. Crozier, A. V. G Chizmeshya and J. D. Smith andJ. Kouvetakis Appl. Phys. Lett. 83, 3489 (2003), which are incorporatedherein by this reference.

In order to fatricate devices using these materials, however, it isnecessary to dope thin films of the materials with donor and acceptorelements, such as B, P, As and Sb. Previously known methods for dopingSi-based semiconductors with As or P have significant limitations.Typically n-doping is performed using a molecular source approach or byion implantation using solid sources of the dopant elements. Ionimplantation has advantages such as relatively low processingtemperatures and the short processing times. However, it also has somemajor disadvantages, such as significant substrate damage andcomposition gradients across the film. For the thermodynamicallyunstable Sn—Ge lattice the re-growth temperatures, that are required torepair the implantation damage of the crystal, may exceed thetemperature stability range of the film, resulting in phase segregationand precipitation of Sn. In addition, with ion implantation there arelimits as to how much dopant can be introduced into the structure. Ionimplantation methods and conventional CVD of the well known PH₃ and AsH₃analogs require severe and often hostile processing conditions and areexpected to be incompatible with the properties and stability range ofthe relatively fragile Ge—Sn lattice. In addition PH₃ and AsH₃ arehighly toxic and in fact can be lethal in relatively small doses.

There is a need, therefore, for a method of incorporating appropriateconcentrations of activated atoms into the lattice of the Ge—Sn systemand in Ge_(1-x-y)Sn_(x)E_(y) (E32 P, As, Sb) semiconductors and relatedSi—Ge—Sn—E and Si—Ge—E analogs. It is an object of the present inventionto provide such a method.

It is another object of the present invention to such a method that ispractical to implement.

Additional objects and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by theinstrumentalities and combinations pointed out herein.

SUMMARY OF THE INVENTION

To achieve the foregoing objects, and in accordance with the purposes ofthe invention as embodied and broadly described in this document, weprovide a novel process for incorporating group V atoms such as P, Asand Sb into. Ge—Sn materials and other group IV semiconductors. Theprocess includes synthesizing a compound having the formula E(GeH₃)₃wherein E is selected from the group consisting of arsenic (As),antimony (Sb) and phosphorus (P). According to a preferred approach,GeH₃Br with [(CH₃)₃Si]₃E are combined under conditions whereby E(GeH₃)₃is obtained. The E(GeH₃)3 is then purified by trap-to-trapfractionation. E(GeH₃)₃ can be obtained with a yield from about 70% toabout 76%.

According to another aspect of the invention, a method for doping aregion of a semiconductor material in a chemical vapor depositionreaction chamber is described. The method includes introducing into thechamber a gaseous precursor having the formula E(GeH₃)₃, wherein E isselected from the group consisting of arsenic (As), antimony (Sb) andphosphorus (P). The semiconductor material can comprise germanium (Ge),SiGeSn, SiGe or SnGe.

According to another aspect of the invention, a method for depositing adoped epitaxial Ge—Sn layer on a substrate in a chemical vapordeposition reaction chamber is described. The method includesintroducing into the chamber a gaseous precursor comprising SnD₄ mixedin H₂ under conditions whereby the epitaxial Ge—Sn layer is formed onthe substrate, including a silicon substrate, and introducing into thechamber a gaseous precursor having the formula E(GeH₃)₃, wherein E isselected from the group consisting of arsenic (As), antimony (Sb) andphosphorus (P). The gaseous precursor is introduced at a temperature ina range of about 250° C. to about 350° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate the presently preferred methodsand embodiments of the invention. Together with the general descriptiongiven above and the detailed description of the preferred methods andembodiments given below, they serve to explain the principles of theinvention.

FIG. 1 shows a typical gas-phase FTIR spectrum of trigermylarsine,(H₃Ge)₃As showing sharp absorption bands at 2077 (Ge—H stretching), 873,829, 785 (Ge—H deformation), 530 and 487 cm⁻¹ (Ge—H rocking).

FIG. 2 shows the PIXE spectrum of a Ge—Sn:As film grown according to thepresent invention.

FIG. 3 is a low energy SIMS profile for Ge—Sn:As (3 at % Asconcentration) grown according to the present invention.

FIG. 4 shows aligned and random RBS spectra represented by the low andhigh intensity traces, respectively, of a 120 nm Ge_(0.97)Sn_(0.03) filmdoped with As grown on Si according to the method of the presentinvention.

FIG. 5 is a low energy SIMS profile of a Sn_(0.03)Ge_(0.97) sample dopedwith As according to the present invention.

FIG. 6 is a cross sectional view of a layer of GeSn;As/Si(100) showing ahighly uniform film thickness and smooth and continuous surfacemorphology.

FIG. 7 is a magnified view of the GeSn;As/Si(100) heterostrucure grownaccording to the invention, showing that most of the defects areconcentrated near the film/substrate interface while the upper portionof the layer remains relatively defect free. The inset shows an electrondiffraction pattern indicating a highly aligned and epitaxial GeSn:Aslayer on Si.

FIG. 7 is a high resolution image of the film/substrate interface of aGe_(0.97)Sn_(0.03):As film grown on Si (100). The image is in the (110)projection and shows high quality heteroepitaxial character.

FIG. 8 is an atomic force microscope image of the aGe_(0.97)Sn_(0.03):As film grown on Si (100) according to the presentinvention.

DESCRIPTION

In this specification, we describe new synthesis strategies, based onnovel molecular hydride sources, to incorporate Group V atoms such as P,As and Sb into the diamond lattice of Group IV semiconductor materials,including the Ge and Si—Ge and SiGeSn systems These sources are thetrigermylphosphine P(GeH₃)₃, trigermylarsine As(GeH₃)₃, andtrigermylstibine Sb(GeH₃)₃ family of compounds. These molecularprecursors are stable and volatile at room temperature and possess thenecessary reactivity to dissociate completely at growth conditions forGe, SiGe, SnGe or SiGeSn systems, via elimination of benign and stablebyproducts that do not contaminate the film. The byproduct is the H₂molecule, indicating that the precursors must be carbon-free inorganichydrides that incorporate the desired elements P, As and Sb within a Gecoordination environment The reactions of these molecules withappropriate concentrations of SnD₄ and/or (GeH₃)₂ will generate Ge—Sncompositions doped with the desired levels of a group V element.

According to one aspect of our invention, the As(GeH₃)₃, Sb(GeH₃)₃, andP(GeH₃)₃ hydride precursors are prepared using a novel high-yieldmethod. These precursors are then used in a novel doping method thatinvolves in situ incorporation of the dopant atoms into the Ge, SiGe,SnGe or SiGeSn system. The hydride compounds are co-deposited withappropriate Si/Ge/Sn sources to form Sn—Ge or Si—Ge—Sn doped with theappropriate carrier type. In the case of As, we have succeeded inincreasing the free carrier concentration by making and using precursorswith direct Ge—As bonds, such as As(GeH₃)₃. This unique species is anideal molecular source for low temperature, low cost, high efficiencydoping applications that are conducted via simple, single-stepprocesses. The compound is carbon-free inorganic hydride and is designedto furnish a basic structural unit comprised of the dopant atomsurrounded by three Ge atoms. This arrangement produces homogeneous,substitution of dopant atoms at high concentrations without clusteringor segregation.

The P(GeH₃)₃, As(GeH₃)₃, and Sb(GeH₃)₃ precursors can be used to dopefunctional materials such as Ge, SiGe, SnGe or SiGeSn at levels thatcannot be achieved by conventional methods. We can increase the freecarrier concentration by using these precursors with direct Ge—P, Ge—As,and Ge—Sb bonds and atomic arrangements that are structurally compatiblewith the Ge—Sn lattice. Previous reports provide only preliminaryresults of the synthesis and some basic physical properties of theseP(GeH₃)₃, As(GeH₃)₃, and Sb(GeH₃)₃ compounds. See S. Cradock, E. A. V.Ebsorth, G. Davidson, L. A Woodard, J. Chem. Soc. A, 8, 1229, (1967); D.W. H. Rankin, A. G. E. Robiet, G. M. Sheldrick, 5 Beagley, T. G. HeMit,J. Inorg. Nucl. Chem., 31, 2351, (1969); E. A. V. Ebswort, D. J.Hutchison, J. Douglas, D. W. H. Rankin, J. Chem. Res., Synop, 12, 393,(1980); E. A. V. Ebsworth, D. W. H. Rankin, G. M. Sheldrick, J. Chem.Soc. A, 11, 2828, (1968). D. E. Wingeleth, A. D. Norman, PhosphonusSulfur, 39, 123, (1988). These previously-described procedures, however,provide low yields and in certain cases only traces of the desiredproduct are produced. In addition these procedures are exceedinglydifficult and involve steps that can be potentially dangerous especiallyfor the scaling up phase of the work to produce industrial-scalequantities of the desired compound. Our work demonstrates new andpractical methods to prepare, isolate, purify and handle these moleculesin sufficient quantities to make them useful as chemical reagents aswell as CVD gas sources for semiconductor applications.

Preparation of (GeH₃)₃P, (Ge H₃)₃As, and (Ge H₃)₃Sb for DopantApplications

Conventional n-doping of semiconductor materials with P or As atoms isperformed by use of molecular PH₃ and AsH₃ (the SbH₃ analog is unstable)or by ion implantation using solid sources of the elements. As discussedabove, ion implantation causes significant substrate damage andcomposition gradients across the film. For the thermodynamicallyunstable Sn—Ge lattice, the re-growth temperatures that will be neededto repair the implantation damage of the Sn—Ge crystal may exceed thetemperature stability range of the film, resulting in phase segregationand precipitation of Sn. Therefore, for doping of the Sn—Ge lattice itis desirable to use a low-temperature molecular source approach sincethe introduction of the dopant takes place in situ during film growthand as host Ge—Sn the lattice is generated.

Using a typical growth process conducted by either gas-source molecularbeam epitaxy (GS-MBE) or chemical vapor deposition (CVD), we chose toco-deposit a compound with the general formula E(GeH₃)₃ (E=P, As, or Sb)along with the host Ge—Sn material. We determined that this growthreaction would eliminate hydrogen and generate in situ the Ge₃Emolecular core, which contains the dopant atom B surrounded by three Goatoms. This arrangement represents a simple compositional and structuralbuilding block of the host lattice. Using the Ge₃E core as the buildingblock would also completely exclude formation of undesirable E-E bondingarrangements that may lead to clustering or segregation of the E dopantspecies. Thus we believed this new approach would be most likely toyield a highly homogeneous random distribution of the dopant at distinctatomic sites throughout the film. Furthermore, the doping levels couldbe precisely controlled by careful adjustment of the flux rate of theprecursor during the course of the layer growth. An important benefit ofAs(GeH₃)₃ [or P(GeH₃)₃] is its higher reactivity compared to AsH₃, whichallows lower depositions temperatures than those employed inconventional CVD doping processes utilizing AsH₃ and related hydrides ofphosphorus.

Numerous publications in the literature deal with synthesis, propertiesand reactions of the compounds (Me₃Si)₃E, (Me₃Ge)₃E, (Me₃Sn)₃E, andNe₃Pb)₃E (E=P, As or Sb), which are the organometallic analogs of thedesired precursors. See G. A. Forsyth, D. W. H. Rankin, H. E. Robertson,J. Mol. Struct. 239, 209, (1990); H. Schumann, H. J. Kroth, Z.Naturforsch., B: Anorg. Chem., Org. Chem. 32B, 523, (1977); G. Becker,H. Freudenblum, O. Mundt, M. Reti, M. Sachs, Synthetic Methods ofOrganometallic and Inorganic Chemistry, 3, 193, (1996); S. Schulz, M.Nieger, J. of Organomet. Chem. 570, 275, (1998); H. Schumann, U. Frank,W. W. Du Mont, F. Marschner, J. Organomet. Chem, 222, 217, (1981); M.Ates, H. J. Breunig, M. Denker, Phosphous, Sulfur Silicon Relate. Elem.102, 287, (1995); H. Schumann, A. Roth, O. Stelzer, M. Schmidt, Inorg.Nucl. Chem. Lett. 2, 311, (1986). These materials have been widelyutilized as common reagents in classical metathesis reactions to producenumerous molecular systems that incorporate the (e₃Si)₂E, (Me₃Ge)₂E, and(Me₃Sn)₂E ligands. However, there has been relatively little activityassociated with the corresponding hydrides (which are completely free ofstrong C—H bonds that introduce carbon contaminants in the films)despite their potential importance as precursors for deposition of novelmicroelectronic and optoelectronic materials.

The (SiH₃)₃E family of molecules has been synthesized and theirproperties have been investigated. See G. Davidson, L. A. Woodward, E.A. V. Ebsworth, G. M; Sheldrick, Spectrochim. Acta, Part A, 23, 2609,(1967); B. Beagley, A. G. Robiette, G. M. Sheldrick, Chem. Commun, 12,601, (1967); A. Blake, B. A. V. Ebsworth, S. G. D. Henderson, ActaCrystallogr., Sect. C. Cryst. Struct. Commun, C47, 489, (1991); H.Siebert, J. Eints, J. Mol. Struct. 4, 23, (1969); D. C. McKean,Spectrochim. Acta, Part A, 24, 1253, (1968); J. B. Drake, J. Simpson, J.Chem. Soc. A. 5 1039, (1968). The high reactivity of the Si—H bonds andthe absence of carbon from the molecular architecture indicated to usthat these compounds could be ideal sources for low temperaturedepositions of semiconductors doped with P and As. The known methods forsynthesizing these compounds, however, are complex and require use andmanipulation of highly toxic, explosive and pyrophoric reagents such asPH₃, AsH₃ and KPH₂. In addition, the reported reaction yields are toolow to even be considered usefull for routine laboratory applications.Thus, we determined that the synthetic routes of these compounds couldnot be viable for large scale industrial use.

On the other hand, there have been very few reports concerning thegermaniun analogs (GeH₃)₃E. See S. Cradock, E. A. V. Ebsorth, G.Davidson, L. A. Woodard, J. Chem. Soc. A, 8, 1229, (1967); D. W. H.Rankin, A. G. E. Robiet, G. M. Sheldrick, 5 Beagley, T. G. Hewit, J.Inorg. Nucl. Chem., 31, 2351, (1969); E. A. V. Ebswort, D. J. Hutchison,J. Douglas, D. W. H. Rankin, J. Chem. Res., Synop, 12, 393, (1980); E.A. V. Bbsworth, D. W. H. Rankin, G. M. Sheldrick, J. Chem. Soc. A, 11,2828, (1968); D. E. Wingeleth, A. D. Norman, Phosphorus Sulfur, 39, 123,(1988). These papers describe initial preparation methods andpreliminary identifications of such compounds. However, the yieldsobtained and the experimental synthetic procedures described are notviable for industrial or laboratory applications. Moreover, we found noreport describing the tin (SnH₃)₃Sn and lead (PbH₃)₃Pb species. Wedecided to investigate (GeH₃)₃P, (GeH₃)₃As, (GeH₃)₃Sb as desirablecompounds for the synthesis of Ge_(1-x-y)Sn_(x)P(As,Sb)_(y) systems.

(GeH₃)₃P has been previously obtained by treating a small excess ofGeH₃Br with (SiH₃)₃P as illustrated by the equation:3 GeH₃Br+(SiH₃)₃P→3SiH₃Br+(GeH₃)₃PNo yield was reported and the product was characterized by hydrogenanalysis, ¹H and ³¹P NMR, IR and mass spectroscopy. (GeH₃)₃P wasdescribed as a colorless liquid with a melting point of −83.8° C. and avapor pressure of 1 mmHg at 0° C. See S. Cradock, B. A. V. Ebsorth, G.Davidson, L. A. Woodard, J. Chem. Soc. A, 8, 1229, (1967); D. W. H.Rankin, A. G. E. Robiet, G. M. Sheldrick, 5 Beagley, T. G. Hewit, J.Inorg. Nucl. Chem., 31, 2351. Before the method of our invention, the(GeH₃)₃As and (GeH₃)₃Sb compounds were prepared in low yields by thereaction of bromogermane with the corresponding silyl compounds (whichas indicated above are difficult to produce in sufficient yields to bepractical reagents for routine laboratory synthesis). See E. A. V.Ebsworth, D. W. H. Rankin, G. M. Shelcick, J. Chem. Soc. A, 11, 2828,(1968). (GeH₃)₃As and (GeH₃)₃Sb were identified and characterized byNMR, IR, and Raman spectroscopies. These molecules were found todecompose very slowly, over time, at room temperature to give germaneand an unidentified involatile substance. Their vapor pressures were notreported but there was mention of distilling the liquids onto CsBrplates to obtain IR spectra, indicating that they are sufficientlyvolatile to allow significant mass transport under vacuum.

(GeH₃)₃P has also been synthesized by the redistribution reaction ofsilylphosphines and germylphosphines in the presence of B₅H₉, asdescribed by Wimgeleth, A. D. Norman, Phosphorus Sulfr, 39, 123, (1988).In these reactions, B₅H₉ and GeH₃PH₂ were intermixed in the gas phase atroom temperature and the trigermylphosphine (20% yield) was found in thereaction vessel along with PH₃, GeH₄, and unreacted starting material.

According to a preferred method of the present invention, we provide anew, convenient and high yield method to prepare (GeH₃)₃P, (Ge H₃)₃As,and (Ge H₃)₃Sb. This trigermyl family of compounds is safer and easierto handle and store than reagents such as PH₃, AsH₃ and KPH₂. This newmethod is based on the general reaction described by the equation below,and provides large concentrations of the final product (>70%) to allowthorough characterization, purification and ultimately routineapplication in film growth. According to this method, the more commonand relatively inexpensive trimethylsilyl derivatives [(CH₃)₃Si)]₃E,{[(CH₃)₃Si)]₃P, [(CH₃)₃Si)]₃As, [(CH₃)₃Si)]₃Sb}, are used as startingmaterials. Straightforward, large scale syntheses of these compounds iswell known to those of skill in the art. The synthesis of E(GeH₃)₃ isachieved by thee reaction of GeH₃Br with [(CH₃)₃Si)]₃E according to thefollowing equation:3 GeH₃Br+[(CH₃)₃Si)]₃E→3(CH₃)₃Si Br+(GeH₃)₃E→(where E=P, As, Sb)GeH₃Br is readily obtained by a single step reaction of GeH₄ with Br₂.The (GeH₃)₃E products are obtained as colorless volatile liquids and arepurified by trap-to-trap fractionation.

Using this method of the present invention, we have obtained yields ofthe (GeH₃)₃E products typically ranging from 70% to 76%. The ¹H NMR andgas phase IR data of the products are consistent with the (GeH₃)₃P,(GeH₃)₃As and (GeH₃)₃Sb molecular structures. These data conclusivelyreveal that we are able to synthesize and purify the desired compounds.FIG. 1 shows a typical gas-phase FTIR spectrum of trigermylarsine,(H₃Ge)₃AS showing sharp absorption bands at 2077 (Ge—H stretching), 873,829, 785 (Ge—H deformation), 530 and 487 cm⁻¹ (Ge—H rocking). The ¹H NMRspectroscopy (not shown) consisted of a sinlet Ge—H response at 3.896ppm. The gas-phase IR spectrum is nearly identical with that of (H₃Ge)₃P(which we synthesized using the same synthetic methodology) with aslight shift in absorption bands to lower wave numbers.

We have used the (GeH₃)₃E compounds synthesized according to thepreferred process described above as dopant sources to perform a surveyof growth experiments to develop new semiconductor films on Si (100)using CVD. An alternative method for generating suitable dopant sourcesinvolves the preparation of the general family of compoundsEH_(x)(GeH₃)_(3-x) where x=1, 2 and E=P, As, Sb. These can besynthesized by reaction of inorganic or organometallic compounds of theB element with alkali germyls such as KGeH₃ or halogenated germanes suchas BrGeH₃. The products can be readily isolated and purified to givesemiconductor grade reagents for in situ doping applications.

The following examples help to further explain the method describedabove. It will be understood, however, that the examples areillustrative of the process and materials of the invention and that theinvention is not limited only to these examples.

CVD Depositions of As(GeH₃)₃

Depositions of pure trigermylarsine (As(GeH₃)₃) via ultra-high vacuumCVD (UHV-CVD) showed that the molecule decomposes on Si (100) attemperatures as low as 350° C. to form thin films with approximately 30at. % As. This indicates that the entire Ge₃As molecular core isincorporated into the deposited material. Low-pressure CVD growth ofAs-doped Ge_(1-x)Sn_(x) films was also demonstrated. Arsenicconcentrations up to 3 at. % were obtained. Doping level incorporationswere also achieved by reactions of appropriate concentrations ofAs(GeH₃)₃.

Our initial growth experiments demonstrated that compositional controlof As in Ge—Sn can be obtained by simply varying the partial pressure ofthe reactant gases As(GeH₃)₃, SnD₄ and Ge₂H₆. We characterized thesample films using RBS to determine the Ge to Sn ratio and usingparticle-induced X-ray emission (PIXE) to determine the Asconcentrations. FIG. 2 shows the PIXE spectrum of sample Ge—Sn:As films.Quantification obtained from fitting the peaks shows that the samplefilms contained about 3 at. % As. We used Secondary Ion MassSpectrometry depth profile analysis (SIMS) to determine the As elementaldistribution and Hall/FTIR ellipsometry measurements to determinecarrier concentrations and effective masses. Initial deposition studieshave shown that As is readily incorporated into the Ge—Sn lattice. Lowenergy SIMS of the samples showed highly homogeneous profiles of As andthe Ge and Sn constituent elements throughout the film. FIG. 3 is a lowenergy SIMS profile for a Ge—Sn:As (3 at % As concentration) sample. Weused TEM to show that the microstructure and epitaxial character of thesample film is of good quality. X-ray diffraction showed that the samplefilm had an average diamond cubic lattice.

Following our initial growth experiments, we performed additionalexperiments using the process of our invention to grow sampleGe_(1-x)Sn_(x) films doped with As atoms to determine optimal growthconditions for yielding high quality layers with crystalline perfectionand phase homogeneity required for many desirable device applications.For these experiments, we utilized UHV-CVD reaction of SnD₄, Ge₂H₆ andAs(GeH₃)₃ at 350° C. Concentrations of the reactants were selected toobtain the desired composition in the alloy.

FIGS. 4-9 show results of our characterization of a resultingGe_(0.97)Sn_(0.03) film doped in situ with arsenic using the As(GeH₃)₃compound as the source of the As atoms. Again, we used Rutherfordbackscattering (RBS) to determine the bulk concentration of theresulting films and low energy SIMS to obtain the As. elemental profile.FIG. 4 shows a typical RBS spectrum of a Ge—Sn sample dope with As. TheGe and Sn concentrations were found to be 97% and 3 at. %, respectively.The As content was determined by SIMS to be 1.71×10²¹ atoms/cm³. Thechanneling for both Ge and Sn is identical, indicating that the materialis single phase and that the elements occupy substitutional sites in thesame average diamond structure. FIG. 5 shows a low energy SIMS profileof a Sn_(0.03)Ge_(0.97) sample doped with As. The elemental profilesindicate that the films have a highly uniform As concentrationthroughout the sample. These SIMS data were used to quantify the dopantcontent using implanted samples of known concentration as a standard,and the As content of the Sn_(0.03)Ge_(0.97) sample was determined to be˜10²¹ atoms per cm³

FIGS. 6-8 show cross sectional electron micrographs of the Ge—Sn:Assample films, which indicate single crystal quality, a high degree ofepitaxial alignment and smooth surface morphology. FIG. 6 is a crosssectional view of the entire layer of a GeSn:As/Si(100) sample showing ahighly uniform film thickness and smooth and continuous surfacemorphology. FIG. 7 is a magnified view of the GeSn:As/Si(100)heterostrucure showing that most of the defects are concentrated nearthe film/substrate interface while the upper portion of the layerremains relatively defect free. The inset of FIG. 7 is a selected areaelectron diffraction pattern which shows that the epitaxial GeSn:Aslayer is highly aligned on the Si substrate. FIG. 8 is a high resolutionimage of the interface in the (110) projection showing high qualityheteroepitaxial character.

Atomic force microscopy was used to examine the surface structure andmorpholoy of the Ge_(0.97)Sn_(0.03):As film. FIG. 9 is an atomic forcemicroscopy (AFM image of such a film, showing extremely smooth surfacetopology with a typical RMS value of 0.7 mn.

CONCLUSION

The above-described invention possesses numerous advantages as describedherein. The invention in its broader aspects is not limited to thespecific details, representative devices, and illustrative examplesshown and described. Those skilled in the art will appreciate thatnumerous changes and modifications may be made to the preferredembodiments of the invention and that such changes and modifications maybe made without departing from the spirit of the invention. It istherefore intended that the appended claims cover all such equivalentvariations as fall within the true spirit and scope of the invention.

1. A method for synthesizing a compound having the formula E(GeH₃)₃wherein E is selected from the group consisting of arsenic (As),antimony (Sb) and phosphorus (P), the method comprising combining GeH₃Brwith [(CH₃)₃Si]₃E under conditions whereby E(GeH₃)₃ is obtained.
 2. Themethod of claim 1 further comprising purifying the obtained E(GeH₃)₃. 3.The method of claim 1 wherein the step of purifying the obtainedE(GeH₃)₃ comprises trap-to-trap fractionation.
 4. The method of claim 1wherein E(GeH₃)₃ is obtained with a yield from about 70% to about 76%.5. A method for synthesizing a compound having the formula E(GeH₃)₃wherein E is selected from the group consisting of arsenic (As),antimony (Sb) and phosphorus (P), the method comprising combining GeH₃Brwith [(CH₃)₃Si]₃E to obtain E(GeH₃)₃ according to the formula:3 GeH₃Br+[(CH₃)₃Si)]₃E→3(CH₃)₃Si Br+(GeH₃)₃E
 6. The method of claim 5further comprising purifying the obtained E(GeH₃)₃.
 7. The method ofclaim 5 wherein the step of purifying the obtained E(GeH₃)₃ comprisestrap-to-trap fractionation.
 8. The method of claim 5 wherein E(GeH₃)₃ isobtained with a yield from about 70% to about 76%.
 9. A method fordoping a region of a semiconductor material in a chemical vapordeposition reaction chamber, the method comprising introducing into thechamber a gaseous precursor having the formula E(GeH₃)₃, wherein E isselected from the group consisting of arsenic (As), antimony (Sb) andphosphorus (P).
 10. The method of claim 9 wherein the semiconductormaterial comprises silicon (Si).
 11. The method of claim 9 wherein thesemiconductor material comprises germanium (Ge).
 12. The method of claim9 wherein the semiconductor material comprises SiGeSn.
 13. The method ofclaim 9 wherein the semiconductor material comprises SnGe.
 14. A methodfor depositing a doped epitaxial Ge—Sn layer on a substrate in achemical vapor deposition reaction chamber, the method comprising:introducing into the chamber a gaseous precursor comprising SnD₄ mixedin H₂ under conditions whereby the epitaxial Ge—Sn layer is formed onthe substrate; and introducing into the chamber a gaseous precursorhaving the formula E(GeH₃)₃, wherein E is selected from the groupconsisting of arsenic (As), antimony (Sb) and phosphorus (P).
 15. Themethod of claim 14 wherein the gaseous precursor is introduced at atemperature in a range of about 250° C. to about 350° C.
 16. The methodof claim 14 wherein the substrate comprises silicon.
 17. The method ofclaim 14 wherein the silicon comprises Si(100).
 18. The method of claim14 wherein the Ge—Sn layer comprises Sn_(x)Ge_(1-x) and x is in a rangefrom about 0.02 to about 0.20.
 19. A method for forming a Group IVsemiconductor film, the method comprising forming the Group IVsemiconductor by a chemical vapor deposition method, said Group IVsemiconductor film being doped with impurities at a concentrationranging from about 10²¹ atoms/cm³ to about several percent, theimpurities being selected from the group consisting of arsenic (As),phosporous (P) and antimony (Sb).
 20. A method for forming a Group IVsemiconductor film, the method comprising: forming the Group IVsemiconductor film by a chemical vapor deposition method; and whileforming the Group IV semiconductor film, doping the film with impuritiesat a concentration ranging from about 10²¹ atoms/cm³ to about 3 at. %,the impurities being selected from the group consisting of arsenic (As),antimony (Sb) and phosphorus (P).
 21. The method for forming a Group IVsemiconductor film according to claim 20, wherein t arsenic (As),antimony (Sb) and phosphorus (P) are added to the Group IV semiconductorfilm by diffusion methods.
 22. The method for forming a Group IVsemiconductor film according to claim 20, wherein said doping stepcomprises introducing the As, P, or Sb impurities into a reactionchamber as hydride compounds, together with at least SnD₄, GeH₄, Ge₂H₆.23. A method of preparing (E)H_(x)(GeH₃)_(3-x), where x=1 or 2 and E isselected from the group consisting of P, As, Sb, the method comprisingreacting inorganic or organometallic compounds of the E element with analkali germyl or a halogenated germane.
 24. The method of preparing(E)H_(x)(GeH₃)_(3-x) according to claim 23 wherein the alkali germylcomprises KGeH₃.
 25. The method of preparing (E)H_(x)(GeH₃)_(3-x)according to claim 23 wherein the halogenated germane comprises BrGeH₃.